yes

I strongly agree with Mark's explanation.

Thanks a lot Mark!

Niwantha , it is also not wrong to say "to you both", but its not necessary if speaking to the couple.

You do not need to say "to you both". If you are speaking to a couple on their Anniversary you are addressing both of them. You would just say, " Happy Anniversary!" or "Congratulations on your Anniversary". If the couple were good friends of mine I might even say, " Happy Anniversary guys!! Well done!" I hope this assists you. Teacher Mark